A solenoid is a common electrical device used to convert electrical energy into mechanical energy. Solenoids are well known in the art and are often utilized as a means of moving a component a predetermined distance at a predetermined time. In its most basic form, a solenoid is an electromechanical device that converts electrical energy into linear or rotary motion. Electrical voltage passes through a coil of insulated copper wire producing a magnetic field, which moves a ferromagnetic plunger located within the core of the coil. Steel parts surround the coil to contain the flux path for maximum pull, push or rotational force. A solenoid can be used to open a valve, activate a switch, apply a brake or a number of other activities where mechanical movement is required and only an electrical energy source is available or practical.
A typical solenoid comprises a steel frame or shell that surrounds the coil of wire and directs the flux path. The coil assembly, when energized with an electrical voltage, creates the magnetic lines of force. A plunger, located within the coil assembly, reacts to the magnetic pull and moves to the center of the coil against a stop or pole piece. The pole piece provides a stop for plunger movement. However, it is often required in a solenoid application that the plunger be retained or held against the pole piece. In order to retain the plunger against the pole piece, a sufficient amount of electrical voltage must be continuously applied to the coil assembly.
To accomplish the plunger hold function, prior art solenoids have included two (2) coil assemblies. A first voltage is applied to the first coil assembly thereby causing the solenoid to perform its work, i.e. the movement of the plunger from its initial position to the pole piece. A second voltage is then applied to the second coil to retain the plunger in its position against the pole piece. The first coil is typically comprised of a heavier gage wire to provide greater ampere turns whereas the second coil is comprised of a lighter gage wire with fewer ampere turns. The first voltage is typically a relatively high voltage and the second voltage is a lower voltage. Solenoids having two coil assemblies have drawbacks including increased expense, increased size, increased weight, and the necessity for entire replacement when one coil burns out (even though the other coil is intact).
Other prior art devices utilize a single coil assembly solenoid, but also provide a control module that applies a high voltage to the coil assembly to perform the work and a lower voltage to the solenoid to perform the hold function. Typically, these dedicated controllers are neither robust nor equipped with versatile connection means to allow use with a broad range of solenoid coils. These prior art devices all exhibit various limitations that the present invention overcomes including a narrow operation voltage range and susceptibility to damage if connected to the power source with improper polarity.
The present invention provides further enhancements in that it allows for direct and continuous connection of the primary power source to the module's power input terminal and also for fixed and continuous connection of the solenoid coil(s) to the module. Control of the application of electrical energy to the solenoid coil(s) can be accomplished by applying a +8 volt to +30 volt (ground reference) low current (less than 10 milliamps) signal to the auxiliary input terminal of the module. This feature allows solenoid systems to be wired without the need for high current switches or relays to control the primary current to the solenoid which in many cases on engine applications exceeds 50 amps.
Other prior art devices utilize an electronic control module that provides a timed application of high energy to the heavier gage winding of a dual winding or dual coil solenoid; however the heavier winding coil becomes inactive after the initial "pull-in" period. Thereafter, the solenoid operates using only the lighter gage coil resulting in low efficiency. In such a system incorrect connections of the control module to the solenoid coils may result in damage to the solenoid and or the control module.
While pulse width modulation has been utilized in the past to control the movement of a solenoid, a pulse width modulation circuit having the structure and benefits, as set forth below, is believed to be novel. The inventor is not aware of any prior art that teaches the unique combination of components and resulting benefits.